During the operation of rotary drilling wells for the extraction of gas and/or oil, a drilling fluid or mud is used to provide lubrication and cooling to the drill bit and to remove cuttings from the bottom of the hole to the surface. This drilling fluid will also control subsurface pressures and isolate migrating fluids from the formation by providing enough hydrostatic pressure, etc. The drilling fluid or mud is pumped down the rotating drill pipe, through the bit and up the annular space between the formation or steel casing and the rotating pipe to the surface.
The drilling fluids can be of any oil based, water based or a combination of oil and water. The non-aqueous fluids include but are not limited to diesel, mineral oils, synthetic oils, unsaturated olefins, organic esters or a combination thereof. Other components such as calcium chloride brine, emulsifying surfactants, rheology modifiers and wetting agents, are also added to the base fluid resulting in a water in oil emulsion, also referred as an invert emulsion. The density of the drilling mud is adjusted with weighing agents such as barite and hematite.
During drilling, the drill bit generates cuttings as it moves forward; these cuttings are small pieces of shale and rock and are transported upwards to the surface in the return flow of the drilling muds to the drilling platform. Other liquid contaminants such as water, brines and crude oil from the formation can get entrained in the drilling muds. Solid and liquid contamination alters the original mud properties causing problems during the operation. In situ equipment such as shale shaker screens and centrifuges remove most of the large particles above 7 microns. However, formation particles that are less than about 5 to 7 microns are more difficult to remove; these are considered the Low Gravity Solids. These LGS can build up in the mud system and cause drilling problems like drill pipe sticking, increased pipe torque, and other high viscosity problems.
Mechanical methods for removing the LGS have been tried like centrifuges; it has been found that long retention times are needed to remove the colloidal particles if they can be removed at all. Thus there is a need for a system that can remove or reduce the LGS while maintaining or improving the mud or emulsion properties for further use. This system could be implemented in situ at the drilling platform or at the mud plants for processing the muds returning from the drilling operations. The need for a comprehensive system where there are no environmental hazards in all the by-products and recycling or disposing does not constitute a threat for the surrounding environment.